1. Field of the Invention
The invention relates to injecting or sparging subcooled water into an FCC feed for enhanced atomization. More particularly, the invention relates to sparging hot, subcooled water into a hotter, lower pressure FCC oil feed, upstream of the feed atomization. The water sparged into the hot oil rapidly vaporizes, forming expanding steam bubbles in the oil and thereby improving the subsequent atomization.
2. Background of the Invention
Atomizing hot, relatively viscous fluids at high flow rates, such as the heavy petroleum oil feeds used in fluidized catalytic cracking (FCC) processes, or fluid cat cracking as it is also called, is an established and widely used process in the petroleum refining industry, primarily for converting high boiling petroleum oils to more valuable lower boiling products, including gasoline and middle distillates such as kerosene, jet and diesel fuel, and heating oil. In an FCC process, the preheated oil feed is mixed with steam or a low molecular weight (e.g., C.sub.4-) gas under pressure, to form a two phase, gas and liquid fluid. This fluid is passed through a pressure-reducing orifice into a lower pressure atomization zone, in which the oil is atomized and brought into contact with a particulate, hot cracking catalyst. In an FCC process, the riser is both the feed atomization zone and the cat cracking zone. Steam is more often used than a light hydrocarbon gas, to reduce the vapor loading on the gas compression facilities and downstream products fractionation. With the trend toward increasing the fraction of the very heavy and viscous residual oils used in FCC feeds, more steam as a fraction of the oil feed is needed for atomization. However, many facilities have limited steam capacity and this constrains their ability to effectively process heavier feeds. Further, the use of steam produces sour water, which must be treated and disposed of. It would be an improvement in the art, if a way could be found to increase the heavy feed cracking capacity of steam limited plants and also to reduce the amount of steam required for atomization.